This invention relates to the lubrication of the contact surface of the axial stop face of a rotor with a stationary housing stop surface, and more particularly to the lubrication of the rubbing contact area between the axial stop face of a turbopump impeller against a cooperating stationary face of the turbopump housing.
Rocket engines, such as the space shuttle main engine, use turbopumps for pumping the liquid hydrogen and liquid oxygen used for providing the combustible propellent. During the main stage operation of the rocket engine, the axial forces on the rotating turbopump shaft, impellers, seals and bearings are balanced by a variable force provided by using a controlled variable pressure balancing cavity and thrust piston. However, during the start-up and shut-down transients, an unbalanced axial force generally results on the impeller or the rotor. When the rotor bearings are incapable of absorbing this unbalanced axial force, the force is absorbed or counter-acted by the action of contact between a face of the rotor, i.e., the axial stop face, against a cooperating or mating backup face on the stationary housing acting as a stop, either or both a forward stationary stop or an aft stationary stop.
The problem presented by this rotational sliding contact at the high speeds and thus severe loads under which such turbopumps function is that high frictional heating and short service lives result. Both hydrogen and oxygen have very little lubricating effect so that excessive wear of the contact surfaces is a particular problem in this environment. Furthermore, and more importantly, frictional heating which results from the sliding contact provides a safety hazard, particularly in the oxygen environment where there is a low threshold of ignition for most metals.
Reinforced synthetic resin polymer, such as that marketed under the brand name Teflon and bronze Teflon bearing cages have been used successfully in liquid oxygen and liquid hydrogen environments to lubricate ball bearings and roller bearings where periodic rubbing contact occurs between the rolling elements and the cage. Thus, it is known that such materials such as Teflon and bronze filled Teflon are suitable for use in the oxygen and hydrogen environments of such turbopumps. However, there are no known means for lubricating the axial stop face and mating housing backup face utilized in such turbopumps.